tunable_create

Create a new system tunable. Tunables allow setting sysctl, loader, or rc variables.

SERVERTruenas SOURCEspranab/truenas-mcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/spranab-truenas-mcp/tunable-create.md

WHAT IT DOES

What tunable_create does on Truenas

AI agents use tunable_create to create or update resources in Truenas, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Truenas environment.

RISK

Why tunable_create is rated Medium

This tool creates new system-level configuration parameters (sysctl, loader, rc variables) that modify kernel and system behavior. While reversible through deletion or reconfiguration, it modifies critical system settings that could affect system stability, performance, security posture, or service behavior. The high severity reflects that misconfiguration could destabilize the NAS or compromise security.

From the tool's definition Create a new system tunable. Tunables allow setting sysctl, loader, or rc variables.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs tunable_create safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Truenas, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For tunable_create, this is the rule to start with:

tunable_create Rate-limited

tunable_create stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "tunable_create": {
      "limits": [
        {
          "counter": "tunable_create_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Truenas, apply this rule, and every tunable_create call is checked against it from then on.

FAQ

Questions about tunable_create

What does the tunable_create tool do? +

Create a new system tunable. Tunables allow setting sysctl, loader, or rc variables. It is categorised as a Write tool in the Truenas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on tunable_create? +

Register the Truenas MCP server in PolicyLayer and add a rule for tunable_create: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Truenas. Nothing to install.

What risk level is tunable_create? +

tunable_create is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit tunable_create? +

Yes. Add a rate_limit block to the tunable_create rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block tunable_create completely? +

Set action: deny in the PolicyLayer policy for tunable_create. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides tunable_create? +

tunable_create is provided by the Truenas MCP server (spranab/truenas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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